South Korea Issues Rare Warning on Currency Surge

SEOUL—South Korea's financial authorities issued a rare warning on Wednesday about the surging Korean currency as the won hit a six-year high against the dollar, which threatens to erode the nation's export competitiveness.

The won has risen about 10% in the past year and is the best-performing Asian currency of 2014.

In a joint message, the Bank of Korea and the finance ministry said they were concerned "about the...